1. Field of the Invention
The present invention relates to an electrode for a lithium-ion secondary battery, a manufacturing method thereof, a lithium-ion secondary battery using the electrode, and a manufacturing method thereof.
2. Background Art
Rechargeable batteries with a non-aqueous electrolyte such as a lithium-ion secondary battery have attracted attention for use in electric vehicles or for energy storage, since the output power is high and the energy density is high. Examples of the application for the electric vehicles include zero-emission electric vehicles without an engine mounted, hybrid electric vehicles with both an engine and a rechargeable battery mounted, and plug-in hybrid electric vehicles charged directly from a system power source. Examples of the energy storage uses include a stationary electric power storage system supplying power stored in advance to desired positions in a state of emergency in which a normal power supply system is out of order.
When the rechargeable batteries are applied to the electric vehicles and the like, output characteristics such as the output power or the energy density and lifetime characteristics are important factors in the relevant fields. Specifically, the lithium ion batteries have a problem in that the capacity of the lithium-ion secondary battery deteriorates by repeating charging and discharging operations over a long period of time. One reason thereof is that a material layer is peeled off from a collector due to expansion and contraction of the volume of an active material accompanying charging-discharging reactions, that is, that the adhesive force between the collector and the material layer (active material layer) is low.
The related techniques in which an adhesive layer or a conductive intermediate layer is interposed between a collector and a material layer so as to solve the above-mentioned problem are disclosed in JP-A-11-73947, JP-A-2004-288520, and JP-A-2008-27633.
In an electrode for a battery disclosed in JP-A-11-73947, an adhesive layer including at least one of an organic titanium compound and a silane coupling agent is formed on a surface of a collector in a dot shape, a stripe shape, or a lattice shape, particularly, so as to improve the adhesiveness between an electrode material layer and a collector in a cathode.
In an anode for a lithium-ion secondary battery disclosed in JP-A-2004-288520, a conductive intermediate layer including conductive particles and a second binder is disposed between a material layer including active material particles containing silicon and/or a silicon alloy and a binder and a metal-foil collector so as to improve conductivity and adhesiveness between the collector and an active material.
In an electrode for a lithium-ion secondary battery disclosed in JP-A-2008-27633, in order to avoid hindrance to electrolytic solution penetration due to swelling and to improve high-rate discharge characteristics (high-output-power characteristics), a first material layer having a large amount of binder (binder components) is formed on a collector, a second material layer having a smaller amount of binder is stacked on the first material layer, and grooves are formed on a surface of the material layer, whereby the binder concentration in the material layer is higher on the surface side than on the collector side.
However, in the electrode for a battery disclosed in JP-A-11-73947, the adhesive force between the material layer and the collector can be enhanced by using at least one of the organic titanium compound and the silane coupling agent as an adhesive, but there is a problem in that since it is very difficult to exclude moisture produced through the reaction from the electrode, the surface of the collector is oxidized to increase the resistance of the battery.
In the anode of a lithium-ion secondary battery disclosed in JP-A-2004-288520, it is possible to achieve the compatibility of the conductivity and the adhesiveness between the metal-foil collector and the material layer by disposing the conductive intermediate layer including the conductive particles and the second binder between the material layer and the metal-foil collector, but the adhesive force between the metal-foil collector and the material layer contributes to the unevenness of the surface of the collector and it is thus necessary to perform a surface treatment on the surface of the collector in advance so as to enhance the adhesive force between the material layer and the collector.
In the electrode for a lithium-ion secondary battery disclosed in JP-A-2008-27633, it is possible to enhance the adhesive force between the collector and the material layer by forming the first material layer having a large amount of binder (binder components) on the collector, but there is a problem in that the conductivity between the material layer (active material) and the collector is lowered because the overall surface of the collector is covered with the material layer having a large amount of binder.